Microelectronic devices, such as semiconductor devices, imagers, and displays, are generally fabricated on and/or in microelectronic workpieces using several different types of machines, otherwise known as tools. Such processing machines often include a plurality of processing stations that perform the same procedures on a plurality of workpieces. Other processing machines include a plurality of processing stations that perform a series of different procedures on individual workpieces or batches of workpieces. For example, these processing stations can be used to carry out electroplating, electrophoretic deposition, electroetching, electropolishing, anodization, or electroless plating procedures. In a typical fabrication process, one or more layers of conductive materials are formed on the workpieces during deposition stages. The workpieces are then typically subjected to etching and/or polishing procedures (e.g., planarization) to remove a portion of the deposited conductive layers and form electrically isolated contacts and/or conductive lines.
Tools that plate, etch, polish and anodize metals or other materials on workpieces are becoming an increasingly useful type of processing machine. These procedures can be used to process copper, solder, gold, silver, platinum, nickel, metal alloys, and other materials that are useful in the manufacture of microfeature workpieces. For example, a typical copper plating process involves depositing a copper seed layer onto the surface of a workpiece using chemical vapor deposition (CVD), physical vapor deposition (PVD), electroless plating processes, or other suitable methods. After forming the seed layer, a blanket layer or patterned layer of copper is plated onto the workpiece by applying an appropriate electrical potential between the seed layer and an anode in the presence of an electroprocessing solution. The workpiece is then cleaned, etched, and/or annealed in subsequent procedures.
In U.S. Application Publication No. 2005/0087439 A1, from which the present application claims priority, it is proposed to employ an electrochemical deposition chamber with a non-porous barrier separating processing fluids. The described chamber is divided into two distinct systems that interact with each other to electroplate a material onto the workpiece while controlling migration of selected components in the processing fluids (e.g., organic additives) across the non-porous barrier. Materials that can be electroplated onto the workpiece include metals that can be placed into an ionic form in the processing fluids. For example, copper, solder, gold, silver, platinum, nickel, metal alloys, and other metals can be deposited onto the workpiece.
A schematic illustration of an electrochemical deposition chamber 10 of application Ser. No. 2005/0087439 A1 is illustrated in FIG. 1. Chamber 10 includes a processing unit 12 that provides a first processing fluid 14, (e.g., a catholyte) to a workpiece 16 (i.e., working electrode), and an electrode unit 18 that provides a second processing fluid 20 (e.g., anolyte) different than the first processing fluid 14, and an electrode 22 (i.e., counterelectrode). The catholyte typically contains components in the form of ionic species such as acid ions and metal ions. The catholyte also includes other components, such as accelerators, suppressors, and levelers which improve the results of the electroplating process. The anolyte includes ionic components such as acid ions and metal ions. Unlike the catholyte, the anolyte typically does not include organic components. Chamber 10 also includes a non-porous barrier 24 between the first processing fluid 14 and the second processing fluid 20. Non-porous barrier 24 allows ions (e.g., H+ and Cu+2) to pass through the barrier, but inhibits organic components (e.g., accelerators, suppressors, and levelers) from passing between the first and second processing fluids. As such, non-porous barrier 24 separates components of the first and second processing fluids from each other such that the first processing fluid can have different chemical characteristics than the second processing fluid. As explained above, the first processing fluid can be a catholyte having organic components and the second processing fluid can be an anolyte without organic components or a much lower concentration of such components. The first processing fluid may also contain metal ions and acid ions at different concentrations than the second processing fluid.
The non-porous barrier of U.S. Application Publication No. 2005/0087439 A1 provides several advantages by substantially preventing the organic components in the catholyte from migrating to the anolyte. First, because organic components from the catholyte are prevented from transferring to the anolyte, they cannot flow past the anode and decompose into products that may interfere with the plating process. Second, because the organic components do not pass from the catholyte to the anolyte and then decompose at the anode, they are consumed at a slower rate so that it is less expensive and easier to control the concentration of organic components in the catholyte. Third, less expensive anodes, such as pure copper anodes or bulk copper material, can be used in the anolyte because the risk of passivation by reaction of the anode with organic components is reduced or eliminated.
As effective as these electrochemical treatment chambers are as processing machines in the fabrication of microelectronic devices on and/or in microelectronic workpieces, for numerous reasons, the chambers are not typically run around the clock. For example, the need to operate the chambers depends on many factors, including the ability of upstream processes to provide a supply of microelectronic workpieces suitable for processing in the electrochemical treatment chambers. When microelectronic workpieces are not available for processing in the electrochemical treatment chambers, the chambers must sit idle.
A drawback of allowing the electrochemical treatment chamber to sit idle without an electric potential provided between the working electrode and the counterelectrode is that the concentration of acid ions and the concentration of metal ions in the catholyte and anolyte can change. In some situations, the change causes the acid ion and metal ion concentration to fall outside of the process specifications. Restarting the electrochemical process with the processing fluids out of specification can result in an inability to achieve satisfactory electrochemical processing of the microfeature workpieces and/or require time consuming and costly steps to bring the processing fluids back into specification.
Another drawback of placing the electrochemical deposition chamber in an idle state without an electric potential present is that organic additives may break down at the non-porous barrier. Such additive breakdown is undesirable because it increases the rate of consumption of the expensive organic additives and introduces undesirable breakdown products into the processing fluids. In addition, steps must be taken to account for the change in additive concentration resulting from the additive breakdown.